i have the same. i sail a freeride board which is 59 wide, and my buddy sails a 62 cm freestyle board. He has 10 L less in volume and he weighs less then me (like 35 K of difference). when i'm sailing 6.2 this guy is usually on 5.5 or 4.2 depending on how overpowered I am and still i have to be seriously overpowered to catch up with him within our 100 m run (we don't have a very wide sail area with SW, on NE we get a 400 m run and i kick his ass only after 300 m). So weight, board width, all factors. and the earlier you plane, the faster you get to your topspeed, but the wider your board, the lower that speed is (usually). You can cath up with this guy after 200 m only because he starts to get controle issues because of his weight when you only start to feel comfortable and want to accelerate.